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P90 Ribosomal S6 Kinase 2 (RSK2) Directly Phosphorylates the 5-HT2A Serotonin Receptor thereby Modulating Signaling

Strachan, Ryan Thomas
http://rave.ohiolink.edu/etdc/view?acc_num=case1247172805

Abstract Details

2009, Doctor of Philosophy, Case Western Reserve University, Biochemistry.
Given the pivotal role G protein-coupled receptors (GPCRs) play in physiological responses, various mechanisms have evolved to ensure the tight regulation of GPCR signaling. Classically, agonist exposure leads to an attenuation of receptor responsiveness (i.e. desensitization) through multiple mechanisms including receptor phosphorylation by second messenger-activated protein kinases (e.g. PKA and PKC) and/or GPCR kinases (i.e. GRKs), receptor internalization, and receptor down-regulation. Our laboratory recently discovered that p90 ribosomal S6 kinase 2 (RSK2), a downstream effector of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) cascade, interacts with the 5-hydroxytryptamine 2A (serotonin 2A, 5-HT2A) receptor and exerts a “tonic brake” on agonist-mediated receptor signaling. Importantly, genetic deletion of RSK2 potentiates 5-HT2A signaling in fibroblasts without affecting its subcellular distribution, global G protein function, and expression of serotonergic pathway genes. Furthermore, re-introduction of wild-type RSK2—but not ‘kinase-dead’ RSK2 (K451A)—into fibroblasts restores normal 5-HT2A signaling. Therefore it was hypothesized that RSK2 regulates 5-HT2A receptor signaling through direct receptor phosphorylation. In this thesis I significantly advanced our understanding of 5-HT2A receptor regulation by showing that RSK2 directly phosphorylates the 5-HT2A receptor third intracellular (i3) loop at the conserved residue Ser314, thereby modulating 5-HT2A receptor signaling. I arrived at these conclusions via multiple lines of evidence including in vitro kinase experiments, tandem mass spectrometry, and site-directed mutagenesis. These findings were further validated using phospho-specific Western blot analysis, metabolic labeling studies and whole-cell signaling experiments. These results support a novel regulatory mechanism whereby a downstream effector of the ERK/MAPK pathway directly interacts with, phosphorylates, and modulates signaling of the 5-HT2A serotonin receptor. Furthermore I discovered that RSK2 differentially regulates 5-HT2A agonist signaling, thereby leading to altered patterns of functional selectivity. These studies ultimately led to the larger discovery that RSK2 is required for receptor tyrosine kinase (RTK)-mediated desensitization of 5-HT2A receptors. It is attractive to speculate that RTK signaling may be relevant for regulating 5-HT2A receptor signaling in vivo given the important role of growth factor signaling in normal physiology. Moreover, this novel regulatory mechanism may have far-reaching implications for human disease in which RTK activity is altered (e.g. neuropsychiatric disorders and cancer).
Bryan Roth, MD, PhD (Advisor)
William Merrick, PhD (Committee Chair)
Martin Snider, PhD (Committee Member)
Paul Ernsberger, PhD (Committee Member)
George Dubyak, PhD (Committee Member)
266 p.
Biochemistry; Pharmacology
serotonin; 5-HT; 5-HT2A; GPCR; RSK; ERK; phosphorylation; RTK; growth factor; functional selectivity; biased agonism

Recommended Citations

Citations

  • Strachan, R. T. (2009). P90 Ribosomal S6 Kinase 2 (RSK2) Directly Phosphorylates the 5-HT2A Serotonin Receptor thereby Modulating Signaling [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1247172805

    APA Style (7th edition)

  • Strachan, Ryan. P90 Ribosomal S6 Kinase 2 (RSK2) Directly Phosphorylates the 5-HT2A Serotonin Receptor thereby Modulating Signaling. 2009. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1247172805.

    MLA Style (8th edition)

  • Strachan, Ryan. "P90 Ribosomal S6 Kinase 2 (RSK2) Directly Phosphorylates the 5-HT2A Serotonin Receptor thereby Modulating Signaling." Doctoral dissertation, Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1247172805

    Chicago Manual of Style (17th edition)

case1247172805
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© 2009, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.